Follow-up type servomotor



` De. 18, 1951 Q w, MORK 2,578,727

FOLLOW-UP TYPE SERVOMOTOR Filed Dec. 23. 1948 /Z-/r 5 Arroz/154x Patented Dec. 18, 195i FoLLow-UP TYPE sERvoMo'roa George W. Mork, South Milwaukee, Wis., assigner to Bucyrus-Erie Company, South Milwaukee, Wis., a corporation of Delaware Application December 23, 1948, Serial No. 67,034

6 Claims.

1 This invention relates to new and useful improvements in servo-motors, by which a powerdriven element is controlled by and follows the motion of a control element which is directly actuated by the operator, and more particularly to servo-motors adapted to utilize pressure fluid (preferably a liquid such as oil) for the actuation of the power-driven element. Such servo-motors are especially suitable for use in actuating brakes or clutches, although it is obvious that the same principle may be employed in other types of mechanism Where follow-up control is desired.

The principal object of this invention is to provide a servo-motor in which the force applied to the power-driven element is determined by the setting of the control element in a manner such that the operator will feel the action of the servo-motor.

A further object is to provide a servo-motor the operation of which is unaffected by back pressurey from other servo-motors or similar devices operating in the same fluid circuit.

A further object is to provide a control valve and control rod therefor which is so designed that in all operating positions fluid pressure thereon is balanced in all directions so that motion of said valve and control element is unaffected by said iiuid pressure.

A further object is to provide a servo-motor all the parts of which are easy to manufacture and can be assembled in a single cylinder unit.

In addition to the above-mentioned objects, a number of novel `and useful details have been worked out, which will be readily Yevident as the description progresses.

The invention consists in the novel parts and in the combination and arrangement thereof, which are deiined in the appended claims, and of which one embodiment is exemplified in the accompanying drawings, which are hereinafter described and explained.

'Throughout the description the same reference number is applied to the same or to similar members.

Figure 1 is a longitudinal section of the servo motor of the invention, with the operatingparts shown in inactive position.

Figure 2 is a similar section with the control element, valve member, andactuated element in position of maximum travel, and the piston in an intermediate position during build-up of pressure uid against the piston face (spring between the piston and the actuated element partly compressed).

Figure .3 is a similar sectionwith the operatingV parts shown in position of maximum travel and maximum force applied to the actuated member (spring between the piston and the actuated element fully compressed).

Figure 4 is a cross-section of the servo-motor, taken along the line -Il of Figure 1.

Figure 5 is a cross-section of the servo-motor taken along the line 5-5 of Figure l.

Turning now to the gures, it is seen that projecting from the upper end of the casing, in the form of a cylinder l i, is a control element, in the form of a rod l2, to which conventional control levers or handles (not shown) may be connected as at iii. Frein the lower end of cylinder l I, there projects an actuated element in the form of a stem t which is designed to be connected, as at l5, to

a brake, clutch, or other actuated member (not shown). Suitable springs may be employed normally to hold the control rod i2 and stem irl in their inactive (oif) position (Figure 1). These springs are not shown because they are well known in the art and usually are applied to the mechanisms to which the rod l2 and stem 4 are connected, rather than directly to the rod l2 and stem le.

Cylinder H has inlet ports i6, Il', and outlet ports i8, i9 the former being connected by passage 2B supplied through a common inlet conduit 2| from. a pressure-fluid source (not shown), and the latter being connected respectively to separate outlet conduits 22 and 23, which are respectively for connection directly to the sump (not shown) and indirectly to the sump through other servomotors or power-fluid driven apparatus in the uid circuit (not shown).

Within the cylinder i l is a single-acting piston 24 which has fluid-tight sliding contact with the cylinder, and comprises a piston head 25 and hollow stem .26. The piston is normally held retracted in inactive position (Figure 1) by piston return spring 2l which acts at one end against the bottom of cylinder i i and at the other end against the bottom of piston stem 2S. The upper end of stem ifi is fitted for limited sliding movement within the hollow end of piston stem 26. Load regulating spring 28, seated at its low-er end on stem M and at its upper end against piston head 25, imposes a force on stem tl that is proportional to the distance moved by the piston from its initial inactive position (Figure 1).

The flow of pressure fluid through the cylinder ports is controlled by valve member 25, which isin the form of a sleeve actuated by control rod l2 and connected thereto by pin 3), and has outwardly fluid-tight sliding contact with 3 the inside of the cylinder at all times, and inwardly fluid-tight sliding contact with the piston when it is in piston-actuating position (Figure 2). Valve member 29 has the following passages to control the flow of uid within and through the cylinder. Transverse passage 3| serves to conduct fluid directly from inlet port I1 to outlet port I8 of the cylinder when the cylinder is in its initial inactive position (Figure 1). Flow through the other cylinder ports is blocked by the valve-sleeve when the valve member 29 is in this initial position. Longitudinal passages 34 in valve member 29 connect the upper and lower chambers 35 and 36 inside the valve member 29 and serve to direct fluid against the piston head 25 when the valve mem,- ber 29 moves downwardly out of its inactive position (Figure 1) into an active position, in which position it uncovers port I6 to allow flow into chamber 35 and blocks flow through cylinder ports I1, I8. in the extreme downward active position (Figures 2 and 3), the lower end 38 of valve member 29 butts against shoulder 33a on the inner wall of cylinder I I. Longitudinal slots 31 in the lower sleeve of valve member 29 serve to conduct pressure uid from the lower chamber 36 of the valve to port I9 and drain conduit 23 when the pressure fluid forces piston head 25 out of engagement with the valve member 29 (Figure 3). Conduit 39, in the wall of cylinder II, connects ports 39a and 3917 at the upper and lower ends of the cylinder chamber in which the valve member 29 travels, and serves to equalize uid pressure in the space 35 above and the space 40 below the valve sleeve so that the valve member is balanced and hence its movement is un.- aiected by the fluid pressure in the assembly. Similarly, control rod I2 is also balanced by passing it through piston head 25 so that both ends of the rod are exposed to atmospheric pressure,

The servo-motor operates in the following manner:

(l) When the valve member 29 and pist-on 2d are in inactive position (Figure l) pressure fluid from inlet conduit 2I is bypassed through cylinder port i1, valve passage 3l, cylinder port I8, and outlet conduit 22 to other working devices in the fluid circuit. The only other inlet port I6 is blocked by valve member 29. Hence no part of the servo-motor is actuated, and how through the servo-motor is unimpeded. Also any back pressure in the circuit will not aiect pressure in the servo-motor so as to actuate it, since the bypassed iiuid is blocked from entering chamber 35.

(2) When the valve member 29 is moved downwai'dly into active position (Figure 2), port I5 is uncovered and ports I1, I8 are blocked by valve member 29, and slots 31 are at the same time covered by piston 24 so that pressure fluid is diverted from the conduit 22, and passes through Cylinder port I6, into upper chamber 35 of the valve and cylinder, thence through valve passages 34 into the lower valve chamber 36 and is directed against the head 25 of piston 2d which blocks any iiow from chamber 35 through slots 31, Under this fluid pressure piston 24 moves downwardly compressing load regulating spring 28 against, and thereby actuating, stem I4 until slots 31 are again uncovered. In this position also back pressure through port i8 cannot affect pressure in the servo-motor.

(3) When the piston head 25 uncovers slots 31 in the lower portion of valve member 29 (Figure 3), fluid iiows out of lower valve chamber S6,

through slots 31, port I9, and conduit 23 to the sump, thereby preventing further increase of pressure against the piston head which is held fixed in this position. Although, in Figure 3, the valve and piston are shown in position of maximum travel, it is obvious that when the valve is moved into any intermediate position, the piston will follow and move into a corresponding position in which the force impressed by the load regulating spring 28 on stem I4 will be directly proportional to the distance the control rod I2, valve member 29, and piston 24 have moved from their initial inactive position.

Having now described and illustrated one form of the invention, it is to be understood that the invention is not to be limited to the specic form or arrangement of parts herein described and shown.

I claim:

l. In a servo-motor, the combination of: a cylinder, an axially slidable piston having outwardly huid-tight contact with said cylinder; a control element; a valve member axially slidably tted within said cylinder and actuated by said control element, said valve member being at will moveable into cooperation with said piston to .direct fluid pressure against said piston and produce follow-up movement of said p-iston; power iluid supply means for supplying power iiuid to said cylinder; power fluid exhaust means for providing unobstructed passage for flow of power uid out of said cylinder when said valve member is withdrawn from cooperation with said piston and also when said piston moves out of such cooperation with said valve member; an actuable element moveable substantially as a unit with said piston, but with a limited amount of relative movement therewith; and resilient means interposed between said piston and said actuable element opposing their relative movement with a force proportional to the displacement of the control element from its inactive position.

2. A servo-motor according to claim l, further characterized by the fact that the valve member in its active positions cooperates with the piston and the cylinder to form a huid-tight pressure chamber; that the power uid supply means includes an inlet port for said cylinder and the power fluid exhaust means includes an outlet port for said cylinder; that the valve member has a passage for conducting flow of power fluid from the inlet port to the outlet port when the valve member is in inactive position; said passage bypassing said chamber when the valve member is in inactive position, whereby fluid pressure in said chamber is independent of the uid pressure in said passage when the valve member is in inactive position; and that said passage is blocked by the cylinder when the valve member is in active position.

3. A servo-motor according to claim 2, further characterized by the fact that the power iiuid supply means also includes a second cylinder inlet port and the power fluid exhaust means includes a second cylinder outlet port; and that power fluid flows through this second pair of ports and through said chamber when the valve member is in active position and the piston is withdrawn therefrom.

4. A servo-motor according to claim 1,` further characterized by the fact that the valve member has outwardly fluid-tight sliding contact with the cylinder and inwardly fluid-tight sliding contact with the piston when it cooperates with the piston; that the power fluid supply means includes a first inlet port for said cylinder and the power fluid exhaust means includes a first outlet port for said cylinder, said rst inlet port being uncovered by the valve member to permit ow of power uid into the cylinder when the valve member is in active position, and said rst outlet port being uncovered by the piston to permit flow from the cylinder when the piston moves out of cooperation with the valve member; that the power fluid supply means also includes a second cylinder inlet port and the power fluid exhaust means also includes a second cylinder out let port, said second ports being blocked by the valve member when the valve member is in active position; and that the valve member has a passage adapted to interconnect the second inlet and outlet ports and bypass from the interior of the cylinder fluid passing through said second inlet and outlet ports.

5. In a servo-motor, the combination of: a cylinder, an axially slidable piston having outwardly fluid-tight contact with said cylinder; an actuable element operatively connected to said piston to move substantially as a unit with said piston; a control element; a valve member axially slidably tted within said cylinder and acltuated by said control element, said valve member being at will moveable into cooperation with said piston to form with said cylinder and piston a fluid-tight chamber; power fluid supply means supplying power uid to said chamber when,l said valve member is in active position, to pro duce follow-up movement of said piston; power iluid exhaust means providing unobstructed passage for power fluid out of said chamber when said valve member is withdrawn from cooperation with said piston and also when said piston moves out of such cooperation with said valve member; and means associated with the valve member to bypass pressure uid around said chamber when the valve member is in inactive position, whereby iiuid pressure in said chamber is independent of the fluid pressure in y said bypass means when the valve member is in inactive position; said bypass means being blocked by cooperation between the valve member and the cylinder when the valve member is in active position.

6. A servo-motor according to claim 5, further characterized by the fact that the valve member has outwardly fluid-tight sliding Contact with the cylinder and inwardly fluid-tight sliding contact with the piston when it cooperates with the piston; that the power iluid supply means includes a first inlet port for said cylinder and the power uid exhaust means includes a lirst outlet port for said cylinder, said rst inlet port being uncovered by the valve member to permit now of power fluid into the cylinder chamber when the valve member is in active position, said iirst outlet port being uncovered by the piston to permit ilow from the cylinder chamber when the piston moves out of cooperation with the valve member; that tile power fluid supply means also includes a second cylinder inlet port and the power fluid exhaust means also includes a second cylinder outlet port, said second ports being blocked by the valve member when the valve member is in active position; and that the valve member has a passage adapted to interconnect the second inlet and outlet ports and bypass from the cylinder chamber fluid passing through said second inlet and outlet ports.

GEORGE W. MORK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 825,866 Rogers July 10, 1906 1,604,545 Bragg et al Oct. 26, 1926 1,790,620 Davis Jan. 27, 1931 1,954,379 Eller Apr. 10, 1934 1,954,427 Platz Apr. 10, 1934 2,107,357 Wood Feb. 8, 1938 2,220,339 Leathem Nov. 5, 1940 2,407,097 Porter Sept. 3, 1946 

